1. Field of the Invention
The present invention relates to a structure for fixing an optical cable holding box to a printed circuit board, also serving for the purpose of preventing occurrence of warping in a large-sized printed circuit board.
2. Description of the Related Art
With the development in recent years of multifunctional transmission apparatus, there are demands for larger-sized printed circuit boards to be mounted in the apparatus. Therefore, production of transmission apparatuses using large-sized printed circuit boards are intensively carried on. However, during the solder dipping process, warping of the printed circuit board becomes more liable to occur the larger in size the printed circuit board is. Therefore, there arises the need for a countermeasure to prevent occurrence of warping in the large-sized printed circuit board. Further, optical transmission systems having large transmission capacity and fitted for high speed transmission are prevalent among transmission systems in use recent years. Hence, there arises the need for holding the excess-length portion of an optical cable in a desired position of the printed circuit board.
FIG. 1 shows a plan view of a conventional art example in which a countermeasure is taken to prevent occurrence of warping in a large-sized printed circuit board. There are provided a pair of horizontally extended (in X direction) warp preventing metal plates 3 fixed to the large-sized printed circuit board 2 in the vicinity of its upper and lower edge portions along the upper and lower edges. On the printed circuit board 2, there are mounted a plurality of electronic parts 4 and an optical module 5. The optical module 5 is connected with an optical cable 6 and the excess-length portion of the optical cable 6 is held in a predetermined position on the large-sized printed circuit board 2 by means of a protection cover 7. Reference numeral 8 denotes a connector.
In the fabrication of large-sized printed circuit boards hitherto in practice, the board with two warp-preventing metal plates 3, extended in X direction, fixed thereto at its upper and lower portions, as shown in FIG. 1, has been dipped in a solder bath. However, since the board is not provided with the warp-preventing metal plates in Y direction (vertical direction), there has been a problem that warping occurs in the vertical direction. Once a warp is formed in the printed circuit board, such trouble becomes liable to occur that the printed circuit board, when inserted into a shelf, does not fit well into the guide groove or the printed circuit board comes into contact with an adjoining printed circuit board.
Further, since the optical cable has so far been held in place by means of the protection cover, it has been unable to mount a part on the portion where the protection cover is fixed and, hence, there has been a problem that the area for holding the excess-length portion of the optical cable therein is fixated. Also when there were provided conditions for mounting parts on the printed circuit board, it has been unable to change at will the holding position of the excess-length portion of the optical cable.